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LFP to 100% Each Week—Assumptions?

Tesla suggests charging the LFP Model 3 to 100% at least once a week to balance voltage and recalibrate range and charge readings.

But I wonder whether this recommendation is based on an assumption of how many miles a typical owner is likely to drive per week. For example, if someone only drives an average of 25 miles per week*, with no particular usage pattern, the car would always be above a 90% SOC.

Do you think the following advice would make more sense:

Charge to 100% every week or every 270 miles**, whichever comes last.

*This describes our situation, since our second car is mostly for emergencies or for the few times my wife and I both need a car.

**Average miles per week driven in US.

Related: https://www.autoevolution.com/news/...charging-the-lfp-batteries-to-100-187075.html
 
Well, in this post , AAKEE gives evidence that
Research shows that LFP has the highest calendar aging around 80-90% and that it is less than at 100%.
It is also lower at or below 70%.
It's the blue asterisk line that's most relevant:

effbaf92-c4cc-4c3e-bca5-b11e4365fb6b-jpeg.872000
 
Well, in this post , AAKEE gives evidence that

It's the blue asterisk line that's most relevant:

effbaf92-c4cc-4c3e-bca5-b11e4365fb6b-jpeg.872000
Correct me if I'm wrong, but that chart relates to generic LFP batteries, that probably aren't in a sophisticated, liquid cooled battery pack, with top and bottom buffers, controlled by an advanced BMS.

We've got real world results from a range of owners and they seem to show ~2-3% degradation after 10-20k miles and ~one year of operation regardless of charging strategy.

The problem is that when you need to use the car, you need to use it. If it's a urgent use case scenario are you really willing to gamble on an inaccurate range prediction, when the car may be at a low state of charge?
 
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AAKEE

Active Member
Jan 8, 2021
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Sweden
Correct me if I'm wrong, but that chart relates to generic LFP batteries,
Well, there is a lot of research reports. Some even used CATL LFP. What we see is that there is very small differences between the research reports.
that probably aren't in a sophisticated, liquid cooled battery pack,
Liquid cooling, or heating doesnt matter when the car is not used. The cell temperature joins the ambient and in the sun the cell pack get about 5-7C higher than the ambient. Sophisticated or not, the batteries can not be protected from calendar aging in the car except cooling to keep them cooler which does not happen)
with top and bottom buffers,
No top buffers on Tesla. Tesla use the battery to the industry standard for 100% SOC —> no top buffer.
Tesla use Bottom buffer. But bottom buffer do not matter for calendar aging, in no way at all.
If someone is shooting at you, a life west and safety belt wont help.
controlled by an advanced BMS.
Which can only sit and watch as the battery degrade from calendar aging.

Calendar aging is [SOC x Celltemp x time]
The BMS can not decide the SOC, the owner do.
The BMS can not decide the cell temp. The environment do. The BMS do not get the authority to cool the cells during hot days.
The BMS can not even stop the time, despite being magic. :)
We've got real world results from a range of owners and they seem to show ~2-3% degradation after 10-20k miles and ~one year of operation regardless of charging strategy.
We need to wait and see a little further.
We can hope that the most recent LFP’s has gotten reduced calendar aging, but we can not be really sure yet. Until then, its better assume things work as before. Even if they has reduced the calendar aging, its probable that things still works about the same way, but slightly less rate.

I have a caviat about that the research can not present data that takes a couple of years to get before the batteries is on the market:
AAKEE’s caviat
Caviat again

The problem is that when you need to use the car, you need to use it. If it's a urgent use case scenario are you really willing to gamble on an inaccurate range prediction, when the car may be at a low state of charge?
I can not write every post so it covers all aspects.
I have written this below soon thousand times:
- I am killing the battery myths. I use research facts to tell the true story of how lithium batteries works, as per the latest research I find. I do not tell anyone how they must use these facts.
-Teslas batteries will hold up anyway, but perhaps with a higher degradation.
- I do not think one should strive so hard to reduce degradation that it kills the joy of having an EV/Tesla. If it feels unpleasant, it is not right.
- It is possible to cut the degradation to half, for the one that would like to do that.
-For the ones that do not care, it might still be good to know the facts and at least know what is good and what is bad instead of having these battery myths. For the ones that care even less, skip reading my posts.
-No one should plan with so low SOC that it causes range anxiety. If avoiding means using 100% SOC, thats OK
-No one should use less then the energy needed for each day. If 100% is needed, OK.
-What is not possible can not be done, so without a charging home possibility some people might need to charge to 90% away from home despite short drives. We can only reduce the degradation in relation to our own conditions.
-Anyone is free to learn about batteries, or not.
-Anyone is free to set their own charging schedule. 50, 80 or 100% its your own choice.

I can reach Superchargers in all possible driving directions so 55% is good enough for me. I also still have a ICE car so non problem for me if the car stands with low SOC (like now, just arrived from my mother in law, 250km / -18C so 11% SOC until charhing commences 0330 in the morning).
 
No top buffers on Tesla. Tesla use the battery to the industry standard for 100% SOC —> no top buffer.
Tesla use Bottom buffer. But bottom buffer do not matter for calendar aging, in no way at all.

What is the industry standard cell level full voltage? I see references to ~3.6V maximum for LFP and from what I can glean from watching charging videos, Tesla allows for ~3.33V maximum.
 
Tesla suggests charging the LFP Model 3 to 100% at least once a week to balance voltage and recalibrate range and charge readings.

But I wonder whether this recommendation is based on an assumption of how many miles a typical owner is likely to drive per week. For example, if someone only drives an average of 25 miles per week*, with no particular usage pattern, the car would always be above a 90% SOC.

*This describes our situation, since our second car is mostly for emergencies or for the few times my wife and I both need a car.

Is the average of 25 miles per week in 25 mile drives, or a 200 mile drive every 8 weeks? How much advance notice do you have for times when you need the second car? I.e. do you have day before notice so that you can charge it to whatever is needed (up to 100%) for the day's driving, or could you need to use the car on quick notice with no opportunity to charge it before? If the latter, are SuperChargers available nearby?
 

AAKEE

Active Member
Jan 8, 2021
1,239
1,865
Sweden
What is the industry standard cell level full voltage? I see references to ~3.6V maximum for LFP and from what I can glean from watching charging videos, Tesla allows for ~3.33V maximum.

No, Tesla do not use any top buffer.

This is a picture taken from this thread:
DE172BDF-5B20-41CC-8DF9-197825893124.png

Cell Voltage Max: 3.642V

Cell voltage only reach the max allowed during charging. After charging with the small load from the car being “on” reduces the Voltage slightly.

CATL LFP:
Max Voltage 3.65V
Mim Voltage 2.5
Nominal voltage 3.2V
1992C460-B93A-4CAA-A569-78BE85459375.jpeg

But as I said in the last post, any top buffer would not help when we are talking calendar aging.

LFP’s Achilles is low capacity. Using buffer in the top would not give any win.
Bottom buffer is there to protect you from getting stranded. As LFP’s is harder to measure the SOC, Tesla sometimes increase the bottom buffer to make sure that it always is a margin of energy left at 0% displayed.
 
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Is the average of 25 miles per week in 25 mile drives, or a 200 mile drive every 8 weeks?

Always short drives. Sixteen miles, one trip, fifty on another trip. Never more than seventy.

How much advance notice do you have for times when you need the second car? I.e. do you have day before notice so that you can charge it to whatever is needed (up to 100%) for the day's driving, or could you need to use the car on quick notice with no opportunity to charge it before?
Always enough notice to charge. Like, "I'm going surfing tomorrow." "Okay, I'll take Tessie to go food shopping."
If the latter, are SuperChargers available nearby?
Thirty miles away.

Thanks for the help brainstorming. It's pretty clear I should charge to 100% and let it drop to 30%. There will be times when it sits over 90% for a week, but I should just live with that.
 
Okay, here's something that would be useful to know:

Let's say you've been really bad, and you haven't charged above 80% for, like, a year of regular use. The BMS is as out of whack as it's possible to be. Now, you start on a trip with the SOC at 50% and keep driving. As your remaining charge decreases, is it likely to

  1. Show you more range than you have
  2. Show you less range than you have
  3. Impossible to know how it will misestimate.
 
Okay, here's something that would be useful to know:

Let's say you've been really bad, and you haven't charged above 80% for, like, a year of regular use. The BMS is as out of whack as it's possible to be. Now, you start on a trip with the SOC at 50% and keep driving. As your remaining charge decreases, is it likely to

  1. Show you more range than you have
  2. Show you less range than you have
  3. Impossible to know how it will misestimate.
Of course, if you keep it plugged in you can always use the app to start the charge remotely and charge it as much as possible before leaving. If you keep the SOC at ~70% you might get to 100% before you leave even on a NEMA 5-20 outlet, or better yet on a shared NEMA 6-50 outlet.
 
That's not meant to be a real world example, just a hypothetical example to help understand how the BMS works without proper calibration.
This is from Tesla:

and this is an interesting article (real world example of an LFP M3 stranded because the BMS was out of calibration):

 
Last edited:
Since you don’t drive long distances range accuracy is not that relevant. I’d just let it go down to 15-20% than charge it back up to 100%. Rinse/Repeat.
Wouldn't it be better to charge to 50% for daily use? Since the OP doesn't drive long distances, range estimates aren't important, and as long as it's staying above 20%, it doesn't matter if the BMS has drifted so much that it's off by 15%. But before driving a long distance, the battery should be topped off to 100% so the BMS again has a reference point.
 
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Wouldn't it be better to charge to 50% for daily use? Since the OP doesn't drive long distances, range estimates aren't important, and as long as it's staying above 20%, it doesn't matter if the BMS has drifted so much that it's off by 15%. But before driving a long distance, the battery should be topped off to 100% so the BMS again has a reference point.
When I get in my car, I need to have confidence that my indicated range %/miles/km estimate is accurate. Life gets in the way of 'it's only driven to church on Sundays' scenarios. Failing to get to where you need to go can have drastic consequences.
 

stopcrazypp

Well-Known Member
Dec 8, 2007
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When I get in my car, I need to have confidence that my indicated range %/miles/km estimate is accurate. Life gets in the way of 'it's only driven to church on Sundays' scenarios. Failing to get to where you need to go can have drastic consequences.
That's you, but OP only drives 25 miles a week, so they have plenty of margin even charging at 50%. Just don't assume the bottom 10% is accurate. I'm pretty sure that can be easily accounted for (just adjust whatever emergency reserve you want up by 10%).
 
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That's you, but OP only drives 25 miles a week, so they have plenty of margin even charging at 50%. Just don't assume the bottom 10% is accurate. I'm pretty sure that can be easily accounted for (just adjust whatever emergency reserve you want up by 10%).
I've lived long enough to know that life constantly gets in the way of such assumptions. Given the small distribution of proven battery degradation from owner reports, it just isn't worth it to put oneself in a situation where the available range is an unknown quantity to the car's own BMS and nav system.
 

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